using System.Security.Cryptography;
using IdentityShroud.Core.Contracts;
using IdentityShroud.Core.Model;
using IdentityShroud.Core.Security;

namespace IdentityShroud.Core.Services;

public class DataEncryptionService(
    IDekEncryptionService dekCryptor) : IDataEncryptionService
{
    public EncryptedValue Encrypt(RealmDek dek, ReadOnlySpan<byte> plain)
    {
        Span<byte> key = stackalloc byte[dekCryptor.GetDecryptedSize(dek.KeyData)];
        try
        {
            dekCryptor.Decrypt(dek.KeyData, key);
            byte[] cipher = Encryption.Encrypt(plain, key);
            return new (dek.Id, cipher);
        }
        finally
        {
            CryptographicOperations.ZeroMemory(key);
        }
    }

    public byte[] Decrypt(IReadOnlyList<RealmDek> deks, EncryptedValue input)
    {
        // Note a missing key SHOULD not happen. If it does happen something has seriously gone wrong like
        // - Old key removed before migration completed (should not be possible)
        // - Wrong keyset because of programming error.
        var dek = deks.SingleOrDefault(d => d.Id == input.DekId)
                  ?? throw new InvalidOperationException("Required key not found");

        Span<byte> key = stackalloc byte[dekCryptor.GetDecryptedSize(dek.KeyData)];
        try
        {
            dekCryptor.Decrypt(dek.KeyData, key);
            byte[] output = new byte[Encryption.GetDecryptedLength(input.Value)];
            Encryption.Decrypt(input.Value, key, output);
            return output;
        }
        finally
        {
            CryptographicOperations.ZeroMemory(key);
        }
    }
}